The present invention relates generally to vehicles having grille airflow shutters and more particularly to grille airflow shutter systems and methods of controlling such systems.
Grille airflow shutters are devices that control the amount of airflow through a front grille of a vehicle. The airflow control is typically based on cooling or warming needs for heat exchangers in a condenser, radiator, fan module (CRFM) located behind the grille. A greater airflow provides for better heat transfer out of the heat exchangers in the CRFM. When reduced or no airflow is desired, the grille airflow shutters are adjusted to block airflow through the grille, and, conversely, when additional air flow is desired the airflow shutters can be adjusted to allow full airflow through the grille.
Grille airflow shutters have been controlled using one of two methods. There are discrete open/shut shutters that only move between the open and shut positions, and the decision to open is based on reaching a particular temperature threshold, with the shutters remaining open continuously above this threshold, and the decision to close is based on dropping below this threshold, where the shutters remain continuously closed. However, this type of system provides less precise airflow control than is desired and may end up with repeated open/closed cycling if the temperature fluctuates around an open/close temperature threshold.
The other type of grille airflow shutter system overcomes the precision concern by using shutters that are variably controlled. That is, the shutters can be controlled to be in various positions of partial closure. With this control, the precise amount of airflow can be achieved by opening the shutters only the desired amount. These variable shutters are controlled with pulse width modulation. However, pulse width modulation, while allowing for the variable control of the shutters, adds significantly to both the cost of the physical hardware and to the complexity of the control algorithm and driver.